Restrict Concurrent Jobs

I’ve got a requirement to integrate into appliances which cannot scale. I was wondering if Zato has any best practices regarding managing this.
To Explain:
A REST service to an appliance server can start a Job that takes some-time™ , then run polling queries to monitor the job until it stops. Both of these could be written as a Zato service class.
I would like to only run 4 of these jobs concurrently and Queue any future requests to this appliance.
Bonus points would be awarded for the ability to adjust this queue… And the ability to change this concurrency limit dynamically…

Sorry if this is already in the docs, but I can’t seem to find guidance on this.